Contents

Voltage Divider

The Arduino reads the voltage at a pin, so in order for the LDR to be read by the Arduino, it needs to affect the voltage. This is done by creating a voltage divider.

Voltage dividers are circuit made of 2 resistors. The resulting voltage is the ratio of those resistors.

By replacing one of the resistors with an LDR, you have made a variable voltage divider dependent on the light level.

Circuit

The below circuit has two LDRs each in a different position within the voltage divider. The resistor value that you choose will vary according to the range of the LDR and the light levels you want to detect. 10kOhms may be a good starting place.